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Abstract:

A turbine blade system including a first turbine blade and a second
turbine blade being arranged adjacent to each other shall be suited to
allow a particularly secure and reliable operation of a turbine. To this
end, the turbine blades are in contact in a first surface area and
separated from each other in a second surface area, wherein the first
turbine blade includes a pocket containing a damping piece in the second
surface area.

Claims:

1.-9. (canceled)

10. A turbine blade system, comprising: a first turbine blade; and a
second turbine blade, wherein each turbine blade has a shrouding band
arranged adjacent to each other, in contact in a first surface area and
separated from each other in a second surface area of the shrouding
bands, wherein the first turbine blade comprises a pocket having a
damping piece in the second surface area, wherein the damping piece
includes a cylindrical shape, and wherein an axis of the cylindrical
shape is inclined in relation to a perpendicular of a surface in an area
of the pocket.

11. The turbine blade system according to claim 10, wherein the first
surface area is inclined in relation to the second surface area.

12. The turbine blade system according to claim 10, wherein an inner
shape of the pocket fits an outer shape of the damping piece.

13. The turbine blade system according to claim 10, wherein a size of the
damping piece in a perpendicular direction of the surface in the area of
the pocket is larger than the separation of the first turbine blade and
the second turbine blade in the area.

14. The turbine blade system according to claim 10, wherein each adjacent
pair of turbine blades of a blade row is in contact in a first surface
area and separated from each other in a second surface area, and wherein
one turbine blade of the adjacent pair comprises one pocket containing a
damping piece in the second surface area.

15. A steam turbine, comprising: a turbine blade system according to
claim 10.

16. The steam turbine according to claim 15, wherein the first surface
area is inclined in relation to the second surface area.

17. The steam turbine according to claim 15, wherein an inner shape of
the pocket fits an outer shape of the damping piece.

18. The steam turbine according to claim 15, wherein a size of the
damping piece in a perpendicular direction of the surface in the area of
the pocket is larger than the separation of the first turbine blade and
the second turbine blade in the area.

19. The steam turbine according to claim 15, wherein each adjacent pair
of turbine blades of a blade row is in contact in a first surface area
and separated from each other in a second surface area, and wherein one
turbine blade of the adjacent pair comprises one pocket containing a
damping piece in the second surface area.

20. A gas turbine, comprising: a turbine blade system according to claim
10.

21. The gas turbine according to claim 20, wherein the first surface area
is inclined in relation to the second surface area.

22. The gas turbine according to claim 20, wherein an inner shape of the
pocket fits an outer shape of the damping piece.

23. The gas turbine according to claim 20, wherein a size of the damping
piece in a perpendicular direction of the surface in the area of the
pocket is larger than the separation of the first turbine blade and the
second turbine blade in the area.

24. The gas turbine according to claim 20, wherein each adjacent pair of
turbine blades of a blade row is in contact in a first surface area and
separated from each other in a second surface area, and wherein one
turbine blade of the adjacent pair comprises one pocket containing a
damping piece in the second surface area.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is the U.S. National Stage of International
Application No. PCT/EP2010/050271, filed Jan. 12, 2010 and claims the
benefit thereof. The International Application claims the benefits of
European Patent Office application No. 09001257.6 EP filed Jan. 29, 2009.
All of the applications are incorporated by reference herein in their
entirety.

FIELD OF INVENTION

[0002] The invention is related to a turbine blade system comprising a
first turbine blade and a second turbine blade being arranged adjacent to
each other. It is further related to a steam turbine and a gas turbine.

BACKGROUND OF INVENTION

[0003] A turbine is a rotary engine that extracts energy from a fluid
flow. The simplest turbines have one moving part, a rotor assembly, which
is a shaft with a number of blades attached along its circumference.
Moving fluid acts on the blades, or the blades react to the flow, so that
they rotate and impart energy to the rotor.

[0004] Power plants usually use steam or gas turbines connected to a
generator for electrical power generation. A gas turbine usually has an
upstream combustor coupled to a downstream turbine, and a combustion
chamber in-between. Energy is added to the gas stream in the combustor,
where compressed air is mixed with fuel and ignited. Combustion increases
temperature, velocity and volume of the gas flow, which is subsequently
directed over the turbine's blades spinning the turbine and powering the
combustor and any connected device.

[0005] Steam turbines use pressurized steam from e. g. a steam generator
as its working fluid. To increase thermal efficiency, the steam can be
expanded in multiple turbine stages. Here, steam flow exits from a high
pressure section of the turbine and is returned to the boiler where
additional superheat is added. The steam then goes back into an
intermediate pressure section of the turbine and continues its expansion.

[0006] Especially in low pressure sections of turbines, large back-end
blades are susceptible to vibratory excitation. In order to limit the
amplitudes occurring in various situations and to prevent damage due to
strong vibration, vibrational dampers are used in some designs. This can
be achieved by e. g. solid body frictional damping between turbine
blades, which limits said vibrations. However, allowing friction to damp
vibration requires relatively loose contact of adjacent turbine blades,
reducing the stability of the turbine blade system.

SUMMARY OF INVENTION

[0007] The problem of the present invention is therefore to provide a
turbine blade system of the abovementioned kind which is suited to allow
a particularly secure and reliable operation of a turbine.

[0008] This problem is solved according to the invention by adjacent
turbine blades each having shrouding bands being in contact in a first
surface area of the shrouding band and being separated from each other in
a second surface area of the shrouding band, wherein the first turbine
blade comprises a pocket containing a damping piece in the second surface
area of the shrouding band.

[0009] The invention is based on the consideration that a particularly
secure and reliable operation of a turbine could be achieved if a stable
and stiff assembly of a turbine blade system could be created which at
the same time allows dampening of vibrational excitations through solid
body friction. However, solutions which utilise design features to couple
all of the blades in a row such as contact between adjacent blades at the
tip, mid height or both serve two opposing purposes: the stiffening of
the assembly and the ability to dissipate vibratory energy by friction in
the contact interface. The stiffening requires proper engagement of the
surfaces with big pressing forces to ensure that no wobbling or
macro-sliding can occur. The ability to damp vibrations requires
relatively loose contact with relatively low pressing force, which can in
turn lead to uncontrolled natural frequencies in the blade assembly.

[0010] To fulfill both of these two opposing sub-functions, it is
suggested to separate both functions into different areas of the surface
of the blades, i. e. a first surface area being in close, properly
engaged contact that secures stiffening of the assembly, and a second
surface area in loose contact that allows vibration damping through
friction. To achieve this, the turbine blades are separated from each
other in the second surface area and the first turbine blade comprises a
pocket containing a damping piece that is properly arranged to allow
friction, yielding mechanical damping.

[0011] In an advantageous embodiment, the first surface area is inclined
in relation to the second surface area. Then, the pressing forces for
each of the surface areas are not parallel to each other and can
therefore be easily adjusted independently. This allows a particularly
exact adjustment of the pressing forces for each surface area and
facilitates the separation of stabilization and vibration damping.

[0012] To allow movement of the damping piece towards the adjacent turbine
blade, the damping piece advantageously has a cylindric shape. The
cross-section of the cylinder can be any geometric shape, e.g. a circle
for easy manufacturing of the piece, or any polygon for proper fitting of
the damping piece into the pocket and its stabilization. A cylindric
shape allows movement of the damping piece in and out of the surface.
Vibration of the blade assembly will lead to relative motion between the
damping piece and the adjacent blade and due to the movability of the
damping piece in the pocket also between the damping piece and the pocket
wall, allowing a particularly good dissipation of vibrational energy
through friction.

[0013] In a further advantageous embodiment, the axis of the cylindric
shape is inclined in relation to the perpendicular of the surface in the
area of the pocket. With properly chosen inclination angle and direction
with respect to the rotor movement, the inclination allows the damping
piece to slide radially outwards of the pocket under the action of
centrifugal force. Due to that it contacts the adjacent turbine blade,
forming a friction surface to dampen vibrations, with the centrifugal
force acting as the pressing force. The strength of pressing force can
then be easily adjusted by choice of the inclination angle. Also,
vibrational excitations are damped by friction due to relative movement
of the damping piece and the leading edge as well as the damping piece
and the pocket walls.

[0014] To increase friction of the damping piece with the pocket walls,
the inner shape of the pocket advantageously fits the outer shape of the
damping piece. This also provides proper hold of the damping piece in
directions parallel to the surface area while at the same time--in case
of a cylindrical damping piece--allowing movement in the direction of the
cylinder axis.

[0015] To further improve the hold and stabilization of the damping piece
inside the pocket and prevent the damping piece from slipping out of the
pocket, the size of the damping piece in perpendicular direction of the
surface in the area of the pocket is advantageously larger than the
separation of the turbine blades in said area.

[0016] In a particularly advantageous embodiment, each adjacent pair of
turbine blades of a blade row of the turbine blade, is arranged as
described above, i. e. is in contact in a first surface area and
separated from each other in a second surface area, and wherein one
turbine blade comprises a pocket containing a damping piece in said
second surface area. This leads to a particularly good vibrational
damping and stability of the whole blade row in a turbine.

[0017] Advantageously, a turbine blade system of the above kind is part of
a steam turbine and or a gas turbine. The combination of stabilization
and vibrational damping in the turbine blade system allows a particularly
secure and reliable operation of a turbine.

[0019] The advantages achieved by the present invention particularly
comprise that by arranging two turbine blades of a turbine blade system
such that they are in contact in a first surface area and separated from
each other in a second surface area, wherein the first turbine blade
comprises a pocket containing a damping piece in the second surface area,
both stabilization and vibrational damping can be accomplished, leading
to a particularly secure and reliable operation of a turbine. A proper
inclination of the pocket allows the damping piece slide against the
adjacent turbine blade under the action of centrifugal force, yielding
mechanical damping through friction between the damping piece and the
adjacent blade and pocket walls. Here, the material of the piece can be
chosen such that fretting and wear is prevented. The required stiffening
is provided by the first surface area in contact with the adjacent blade.
Furthermore, the damping piece feature can be used for a variety of
turbine blade designs such as interlocked and free-standing blades.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] An embodiment of the present invention is illustrated in detail in
the following figure.

[0022]FIG. 2 shows the turbine blade system in a circumtangential view.

[0023] All parts have the same reference signs in both FIGs.

DETAILED DESCRIPTION OF INVENTION

[0024] The turbine blade system 1 according to FIG. 1 comprises a first
turbine blade 2 and a second turbine blade 4 that are arranged next to
each other. FIG. 1 shows a cross-section of the turbine blades 2, 4,
viewed in radial direction towards the turbine axis. The FIG. 1 shows a
shrouding band of the first turbine blade 2 and the second turbine blade
4.

[0025] To ensure stability of the turbine blade system 1 during operation
of the turbine, the shrouding bands of turbine blades 2, 4 are arranged
in close contact in a first surface area 6. Here, a relatively big
pressing force is impinged on the surface area 6 which ensures proper
engagement of the turbine blades 2, 4 and stiffening of the turbine blade
system 1 to avoid wobbling and sliding during turbine operation.

[0026] The close contact of the turbine blades 2, 4 in the first surface
area 6 yields the danger of uncontrolled vibrational excitation of the
turbine blade system 1. To avoid this, the turbine blades 2, 4 are
separated from each other in a second surface area 8 and the first
turbine blade comprises a pocket 10 which contains a damping piece 12.
The damping piece 12 has a cylindrical shape fitting the walls 14 of the
pocket 10, so that the damping piece 12 is movable inside the pocket 10.
However, the length of the damping piece 12 is chosen to be long enough
to ensure a proper hold of the damping piece 12 in the pocket 10. The
material of the damping piece 12 is chosen such that fretting and wear is
prevented.

[0027] The damping piece 12 is in contact with the second turbine blade 4,
however due to the movable design of the damping piece 12, the contact is
relatively loose. Vibrational excitations of the turbine blade system 1
will lead to relative motion of the damping piece 12 and the second
turbine blade 4 at their contact surface 16 as well as the damping piece
12 and the pocket walls 14. The resulting friction leads to dissipation
of the vibrational energy and consequently to a damping of the vibration.

[0028] The surface areas 6, 8 are inclined with respect to each other,
such that a force perpendicular to the surface area 6 is not necessarily
implying the same force on the surface area 8. Therefore the pressing
forces for both surface areas 6, 8 can be chosen independently.

[0029]FIG. 2 shows a circumtangential view of the first turbine blade 2,
showing the surface areas 6, 8, the pocket 10 and the cylindrical damping
piece 12. The axis 18 of the cylindrical damping piece 12 is inclined
with respect to the perpendicular of the surface of the turbine blade 2
in the area of the pocket 10. Thus, when the turbine is in motion, the
damping piece slides out of the pocket 10 under the action of centrifugal
force. The centrifugal force presses the damping piece 10 against the
second turbine blade 4. The angle of the inclination can be chosen such
that the desired force is acting on the contact surface 16.

[0030] In a turbine blade system 1 as shown above, the functions of
stabilization and vibrational damping are separated on different surface
areas 6, 8. This leads to a better stiffening of the turbine blade system
1 while at the same time allowing vibrational damping through solid-body
friction, allowing a safer and more reliable operation of a turbine.